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2005 chevy trailblazer_ls
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Discussion Starter · #1 ·
WARNING: This post may make me sound like a complete idiot, but you never get answers if you don't ask the questions...

So this weekend I took a 350 mile trip to Southern Utah. I'm not sure if the transmission is supposed to be doing this or not, but the transmission would do a half-downshift (torque converter unlocking?) under the slightest load, either going up a very shallow incline or sometimes even trying to keep a constant speed. Then it would take a long time for the TC to lock up again. Sometimes I would have to take my foot completely off the gas pedal or be going downhill to get it to lock. Going up steeper hills, I would give the gas pedal an extra push to get the full downshift to 3rd so I didn't burn up the TC.

I have lifted my TB and have 265/75/16 tires and had the shift firmness upgraded to #2 by PCMforLESS. Also, my speedometer doesn't seem to have been recalibrated for the larger tires because it reads 60 mph when I am moving at 65 (GPS verified).

So now to the dumb questions: Is that half-downshift in fact the TC unlocking? If so, will it damage the TC if it runs unlocked for long periods of time or is that normal? Will a shift kit keep the TC from unlocking so easily? Could the funny shifting possibly be the transmission trying to compensate for what the PCM is sensing as low MPH for the RPM the engine is running at? If I get the speedo recalibrated for the larger tires, could that keep the transmission from shifting so erratically?

Again, this could just be normal operation of the transmission, I just didn't have the TB very long before I put the lift, larger tires, and tuned PCM on so I can't remember how it behaved when it was all stock. Thanks!
 

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2002 chevy
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I did a core exchange. PCMforLESS took care of everything.
no i ment what tune program did pcm4less used on your truck? Back then they use to use efilive as their tuner program but now ive heard that they use hptuners. It might play a role on the tune for our trucks. Ask pcm4less and let us know.
 

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2005 chevy trailblazer_ls
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Discussion Starter · #11 ·
Just an update...

Going back down to Southern Utah thursday night for the 4th weekend. Got the tuned stock PCM back and it still reads 3 mph under at 70. Scan gauge is reading same as the speedo.

Noticed something interesting before putting the tuned stock PCM back in. The speedo read under compared to GPS, but the Scan Gauge read the same as the GPS. Haven't had a chance to put the other PCM back in to verify this. Will swap them out tonight and see if the Scan Gauge still matches the GPS.
 

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Have you ever gotten an answer to your original question? I have the same problem, which I raised in a new thread. My TC seems to unlock, the engine revs, but it doesn't seem to make a complete downshift to 3rd.

Any ideas would be helpful.
 

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Discussion Starter · #14 ·
I haven't really found an answer or solution. I just installed a transmission cooler to help with the temperature problem. I also sent one of my PCM's back to have all the transmission mods removed. I won't have that PCM back until next week though. I will repost when I get it in and have a chance to test it out.
 

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2007 chevy trailblazer_ls
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I find it odd that both of you have the same issue, and both have the PCM's tuned... I wonder if something changed from the year that PCM4less did their tune software for this trans, and something's not jiving...

Mike
 

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I find it odd that both of you have the same issue, and both have the PCM's tuned... I wonder if something changed from the year that PCM4less did their tune software for this trans, and something's not jiving...

Mike
It NOT pcmforless's fault! your right it might have to do something with the verisons of the software. the old version worked for me but the new one is messing up my system.
 

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Discussion Starter · #17 ·
Count JamesDowning in as well...

He was having the same TC issues. He swapped his tuned PCM out for the stock one and all of the issues went away. That's why I decided to have my transmission settings returned to stock.
 

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I don't think the pcm tune is the problem. In fact, I had this "hunting" issue prior to getting the tune, and was hoping that it would help. The pcm tune certainly made the shifts crisper, but did not help this issue.

I keep thinking that some type of transmission mod will solve this issue, but am not sure.
 

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2007 chevy trailblazer_ls
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I don't think the pcm tune is the problem. In fact, I had this "hunting" issue prior to getting the tune, and was hoping that it would help. The pcm tune certainly made the shifts crisper, but did not help this issue.

I keep thinking that some type of transmission mod will solve this issue, but am not sure.
hmmm... what does it feel like when you manually move the shifter to 3rd, while it's doing the hunting??

Mike
 
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